Human aging is associated with glucose intolerance and changes in insulin sensitivity but age effects on pancreatic beta cell function in humans are not clear. In healthy young people pancreatic beta cell function adapts to insulin resistance by increasing sensitivity to glucose resulting in increased insulin secretion. Insulin sensitivity can be changed by several pharmacological agents one of which is nicotinic acid which induces insulin resistance and enhances insulin secretion responses in healthy young adults. We propose to study insulin secretion responses of young and elderly subjects (with and without impaired glucose tolerance) before and after nicotinic acid administration to test the hypothesis that aging causes impaired pancreatic beta cell adaptation to insulin resistance.